In Summary:

Think of your planned web site the way you would a new retail outlet. Do some market research to find out what your customers want. The shop should look good from the outside. It should attract customers in from the first page. Once in, they should find plenty of stuff to make them stay and it should always be easy for them to find what they want.

Promote the web site the way you would promote a new shop and integrate it into your overall marketing strategy. Consider advertising on the net using banner ads on other sites. Don't expect your ranking on search engines to increase traffic from casual surfers, but don't neglect it either.